The Greenland Ice Sheet is close to a melting point of no return
Once we emit about 1000 gigatons of carbon, much of the massive ice sheet
will melt irreversibly: We've emitted 500 gigatons so far

Date:
March 27, 2023
Source:
American Geophysical Union
Summary:
A new study using simulations identified two tipping points for
the Greenland Ice Sheet: releasing 1000 gigatons of carbon into
the atmosphere will cause the southern portion of the ice sheet to
melt; about 2500 gigatons of carbon means permanent loss of nearly
the entire ice sheet. Having emitted about 500 gigatons of carbon,
we're about halfway to the first tipping point.


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FULL STORY ==========================================================================
The Greenland Ice Sheet covers 1.7 million square kilometers (660,200
square miles) in the Arctic. If it melts entirely, global sea level
would rise about 7 meters (23 feet), but scientists aren't sure how
quickly the ice sheet could melt. Modeling tipping points, which are
critical thresholds where a system behavior irreversibly changes, helps researchers find out when that melt might occur.


========================================================================== Based in part on carbon emissions, a new study using simulations
identified two tipping points for the Greenland Ice Sheet: releasing 1000 gigatons of carbon into the atmosphere will cause the southern portion
of the ice sheet to melt; about 2500 gigatons of carbon means permanent
loss of nearly the entire ice sheet.

Having emitted about 500 gigatons of carbon, we're about halfway to the
first tipping point.

"The first tipping point is not far from today's climate conditions,
so we're in danger of crossing it," said Dennis Ho"ning, a climate
scientist at the Potsdam Institute for Climate Impact Research who led
the study. "Once we start sliding, we will fall off this cliff and cannot
climb back up." The study was published in AGU's journal Geophysical
Research Letters, which publishes short-format, high-impact research
spanning the Earth and space sciences.

The Greenland Ice Sheet is already melting; between 2003 and 2016, it
lost about 255 gigatons (billions of tons) of ice each year. Much of
the melt to date has been in the southern part of the ice sheet. Air
and water temperature, ocean currents, precipitation and other factors
all determine how quickly the ice sheet melts and where it loses ice.

The complexity of how those factors influence each other, along with the
long timescales scientists need to consider for melting an ice sheet of
this size, make it difficult to predict how the ice sheet will respond
to different climate and carbon emissions scenarios.

Previous research identified global warming of between 1 degree to 3
degrees Celsius (1.8 to 5.4 degrees Fahrenheit) as the threshold beyond
which the Greenland Ice Sheet will melt irreversibly.

To more comprehensively model how the ice sheet's response to
climate could evolve over time, Ho"ning's new study for the first
time used a complex model of the whole Earth system, which includes
all the key climate feedback processes, paired with a model of ice
sheet behavior. They first used simulations with constant temperatures
to find equilibrium states of the ice sheet, or points where ice loss
equaled ice gain. Then they ran a set of 20,000-year-long simulations
with carbon emissions ranging from 0 to 4000 gigatons of carbon.

From among those simulations, the researchers derived the 1000-gigaton
carbon tipping point for the melting of the southern portion of the ice
sheet and the even more perilous 2,500-gigaton carbon tipping point for
the disappearance of nearly the entire ice sheet.

As the ice sheet melts, its surface will be at ever-lower elevations,
exposed to warmer air temperatures. Warmer air temperatures accelerate
melt, making it drop and warm further. Global air temperatures have to
remain elevated for hundreds of years or even longer for this feedback
loop to become effective; a quick blip of 2 degrees Celsius (3.6 degrees Fahrenheit) wouldn't trigger it, Ho"ning said. But once the ice crosses
the threshold, it would inevitably continue to melt. Even if atmospheric
carbon dioxide were reduced to pre- industrial levels, it wouldn't be
enough to allow the ice sheet to regrow substantially.

"We cannot continue carbon emissions at the same rate for much longer
without risking crossing the tipping points," Ho"ning said. "Most of
the ice sheet melting won't occur in the next decade, but it won't be
too long before we will not be able to work against it anymore."
* RELATED_TOPICS
o Earth_&_Climate
# Global_Warming # Climate # Snow_and_Avalanches #
Ice_Ages
o Fossils_&_Ruins
# Early_Climate # Ancient_DNA # Evolution # Origin_of_Life
* RELATED_TERMS
o Ice_sheet o Greenland_ice_sheet o Antarctic_ice_sheet o
Ice_shelf o Carbon_dioxide o Ice_age o Carbon_dioxide_sink
o Carbon_cycle

========================================================================== Story Source: Materials provided by American_Geophysical_Union. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Dennis Ho"ning, Matteo Willeit, Reinhard Calov, Volker Klemann,
Meike
Bagge, Andrey Ganopolski. Multistability and Transient Response of
the Greenland Ice Sheet to Anthropogenic CO 2 Emissions. Geophysical
Research Letters, 2023; 50 (6) DOI: 10.1029/2022GL101827 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/03/230327163212.htm

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